Enclosures and cages for circuit boards have found great popularity due to their modularity. In recent times, circuit boards themselves have become more densely populated. That is, the number of components per circuit board continues to increase.
With greater component density, more heat is generated. But the volume in which to house the circuit boards has not increased. In fact, for certain applications there is a greater demand for smaller and smaller circuit board cages.
Since heat is being generated at an ever increasing rate and the volume of the enclosure cavity continues to decrease, solving the circuit board cage and enclosure cooling problem has become more difficult. Circuit board cage design has become more complex, and cooling these cages has become an art.
The prior art is replete with systems that increase cooling capacity of circuit board cages. All of them, however, lack the sort of heat removal capacity that is now required in high density applications.
In a standard VME (Versa Module European) chassis, heat generated by 1,000 watts to 1,500 watts of power must be removed. It is desirable to operate such systems within a strict temperature range featuring a temperature rise of only approximately 10 degrees Fahrenheit from a quiescent state. This narrow temperature differential, while necessary to ensure long component life, is increasingly difficult to achieve. In some cage designs, this objective is almost all but impossible to accomplish. Standard air flow procedures and cage designs simply no longer provide enough cooling for these high density systems.
Traditionally, so-called Muffin fans have been used to circulate air in these environments. But Muffin (tubaxial) fans are notoriously inefficient, and do not provide even air distribution. They generally provide a dead distribution profile at the hub, and a greater air flow capacity towards the edges of the blades.